In this type of technical field, the next-generation communication schemes, which may become successors of W-CDMA or HSDPA, are being discussed by standardization group 3GPP for W-CDMA. A typical one of the next-generation communication schemes is LTE (Long Term Evolution). As radio access schemes in the LTE, OFDM (Orthogonal Frequency Division Multiple Access) and SC-FDMA (Single-Carrier Frequency Division Multiple Access) are used in downlinks and uplinks, respectively. See non-patent documents 1 and 2, for example. For convenience, the LTE is illustratively described below, but the present invention is not limited to the specific system.
The OFDM is a multi-carrier based technique for transmitting data in several smaller frequency bands (subcarriers) resulting from segmentation of a frequency band. By arranging the subcarriers on the frequency densely without mutual interference while overlapping the subcarriers partially, it is possible to realize fast transmissions and improve utilization efficiency of the frequency.
The SC-FDMA is a single-carrier based technique where Fourier transform and inverse Fourier transform are applied to segment a frequency band, so that several terminals can use the segmented different frequency bands. The SC-FDMA scheme has characteristics of reduction in inter-terminal interference, smaller variations of transmit power and so on. As a result, it is advantageous to reduction in power consumption, wider coverage and so on.
In LTE systems, one or more physical channels are shared in both uplink and downlink communications among several mobile stations (user apparatuses). The channels shared among the several mobile stations are generally referred to as shared channels. In the LTE, the channels are PUSCH (Physical Uplink Shared Channel) for uplinks and PDSCH (Physical Downlink Shared Channel) for downlinks. Also, transport channels mapped into the PUSCH and the PDSCH are referred to as a UL-SCH (Uplink-Shared Channel) and a DL-SCH (Downlink-Shared Channel), respectively.
Also, it is necessary in communication systems using the above-mentioned shared channels to signal which of the shared channels is to be assigned to which mobile stations for each subframe. In the LTE, control channels for the signaling are referred to as a PDCCH (Physical Downlink Control Channel). The above PDCCH is also referred to as a downlink L1/L2 control channel or downlink control information (DCI). The PDCCH includes information pieces such as a DL/UL scheduling grant and a TPC (Transmission Power Control) bit. See non-patent document 3.
More specifically, the DL scheduling grant may include downlink resource block assignment information, an ID of a user apparatus or user equipment (UE), the number of streams, information on precoding vectors, information on a data size and a modulation scheme, information on HARQ (Hybrid Automatic Repeat reQuest) and so on. The DL scheduling grant may be referred to as DL assignment information, DL scheduling information and so on.
Also, the UL scheduling grant may include uplink resource block assignment information, an ID of a user apparatus or user equipment (UE), information on a data size and a modulation scheme, uplink transmit power information, information on a demodulation reference signal and so on.
The above PDCCH is mapped into the first one to three OFDM symbols in 14 OFDM symbols within one subframe, for example. It is specified how many leading OFDM symbols the PDCCH are to be mapped into through a PCFICH described below, which is indicated to a mobile station.
Also, the PCFICH (Physical Control Format Indicator Channel) and a PHICH (Physical Hybrid ARQ Indicator Channel) are also transmitted in the OFDM symbols including the PDCCH.
The PCFICH is a signal for indicating the number of OFDM symbols including the PDCCH to a mobile station. The PCFICH may be referred to as a DL L1/L2 control format indicator. The PHICH is a channel for transmitting acknowledgement information for the PUSCH. The acknowledgment information has ACK (Acknowledgement) as a positive response and NACK (Negative Acknowledgement) as a negative response.
In downlinks, the PDCCH, the PCFICH and the PHICH are mapped into the first M symbols (M=1, 2 or 3) within one subframe. Then, transmit power control is applied to each of these channels to achieve efficient multiplexing and transmission.
Non-patent document 1: 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA”, June 2006
Non-patent document 2: 3GPP TS 36.211 (V8.1.0), “Physical Channels and Modulation”, November 2007
Non-patent document 3: 3GPP TS 36.300 (V8.2.0), “E-UTRA and E-UTRAN Overall description”, September 2007